Linux Fu: File Aliases, Links, and Mappings

Have you heard it said that everything in Linux is a file? That is largely true, and that’s why the ability to manipulate files is crucial to mastering Linux Fu.

One thing that makes a Linux filesystem so versatile is the ability for a file to be many places at once. It boils down to keeping the file in one place but using it in another. This is handy to keep disk access snappy, to modify a running system, or merely to keep things organized in a way that suits your needs.

There are several key features that lend to this versatility: links, bind mounts, and user space file systems immediately come to mind. Let’s take a look at how these work and how you’ll often see them used.

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Linux Fu: Regular Expressions

If you consider yourself a good cook, you may or may not know how to make a souffle or baklava. But there are certain things you probably do know how to do that form the basis of many recipes. For example, you can probably boil water, crack an egg, and brown meat. With Linux or Unix systems, you can make the same observation. You might not know how to set up a Wayland server or write a kernel module. But there are certain core skills like file manipulation and editing that will serve you no matter what you do. One of the pervasive skills that often gives people trouble is regular expressions. Many programs use these as a way to specify search patterns, usually in text strings such as files.

If you aren’t comfortable with regular expressions, that’s easy to fix. They aren’t that hard to learn and there are some great tools to help you. Many tools use regular expressions and the core syntax is the same. The source of confusion is that the details beyond core syntax have variations.

Let’s look at the foundation you need to understand regular expression well.

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Software Development in… Bash

Truly good ideas tend to apply in all situations. The phrase is “never run with scissors”, not “don’t run with scissors unless you are just going into the next room.” Software development methodology is a good idea and most of us have our choice of tools. But what if you are developing a significant amount of bash or similar script? Should you just wing it because bash isn’t a “real” programming language? [Oscar] says no, and if you are writing more than two or three lines of script, we agree.

We’ve made the argument before (and many of you have disagreed) that bash is a programming language. Maybe not the greatest and certainly not the sexiest, but bash is near ubiquitous on certain kinds of systems and for many tasks is pretty productive. [Oscar] shows how he uses a source code formatter, a linter, and a unit test framework to bring bash scripting in line with modern software development. We are pretty sure he uses source control, too, but that seems so elementary that it doesn’t come up outside of a link to his repository in GitHub.

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Linux Adds CH341 GPIO

There was a time when USB to serial hardware meant one company: FTDI. But today there are quite a few to choose from and one of the most common ones is the WCH CH341. There’s been support for these chips in Linux for a while, but only for use as a communication port. The device actually has RS232, I2C, SPI, and 8 general purpose I/O (GPIO) pins. [ZooBaB] took an out-of-tree driver that exposes the GPIO, and got it working with some frightening-looking CH341 boards.

He had to make a slight mod to the driver to get six GPIOs in /sys/class/gpio. Once there though, it is easy to manipulate the pins using a shell script or anything that can write to the virtual files corresponding to the GPIO pins.

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Linux Fu: A Little Help for Bash

It isn’t uncommon these days for a programmer’s editor to offer you help about what you are typing, ranging from a pop up with choices to a full-blown code template. If you have written a million lines of code in the language, this might even annoy you. However, if you use it only occasionally, these can be very helpful. I’ve used Unix and Linux for many years, but I realize that there are people who don’t use it every day. With the Raspberry Pi, Linux servers, and Windows 10 having a bash shell, there are more people using a shell “every once in a while” than ever before. Could you use a little help? If so, you might try bashelp: a little something I put together while writing about bash completion.

There’s good news and bad news. The good news is that Unix has a built-in help command — man — and has for some time. The bad news is that you need to stop what you are typing and enter a man command to use it. Man, by the way, is short for manual.

There are GUI front-ends to man (like yelp, on the left) and you can even use a web browser locally or remotely. However, none of these are connected to what you are typing. You have to move to another window, enter your search term, then go back to your typing. That got me to thinking about how to get a sort of context-sensitive inline help for bash.

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Making the Case for Slackware in 2018

If you started using GNU/Linux in the last 10 years or so, there’s a very good chance your first distribution was Ubuntu. But despite what you may have heard on some of the elitist Linux message boards and communities out there, there’s nothing wrong with that. The most important thing is simply that you’re using Free and Open Source Software (FOSS). The how and why is less critical, and in the end really boils down to personal preference. If you would rather take the “easy” route, who is anyone else to judge?

Having said that, such options have not always been available. When I first started using Linux full time, the big news was that the kernel was about to get support for USB Mass Storage devices. I don’t mean like a particular Mass Storage device either, I mean the actual concept of it. Before that point, USB on Linux was mainly just used for mice and keyboards. So while I might not be able to claim the same Linux Greybeard status as the folks who installed via floppies on an i386, it’s safe to say I missed the era of “easy” Linux by a wide margin.

But I don’t envy those who made the switch under slightly rosier circumstances. Quite the opposite. I believe my understanding of the core Unix/Linux philosophy is much stronger because I had to “tough it” through the early days. When pursuits such as mastering your init system and compiling a vanilla kernel from source weren’t considered nerdy extravagance but necessary aspects of running a reliable system.

So what should you do if you’re looking for the “classic” Linux experience? Where automatic configuration is a dirty word, and every aspect of your system can be manipulated with nothing more exotic than a text editor? It just so happens there is a distribution of Linux that has largely gone unchanged for the last couple of decades: Slackware. Let’s take a look at its origins, and what I think is a very bright future.

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Linux Fu: Custom Bash Command Completion

If you aren’t a Linux user and you watch someone who knows what they are doing use Bash — the popular command line interpreter — you might get the impression they type much faster than they actually do. That’s because experienced Linux users know that pressing the tab key will tend to complete what they are typing, so you can type just a few characters and get a much longer line of text. The feature is very smart so you may not have realized it, but it knows a good bit about what you could type. For example, if you try to unzip a file, it knows the expected file name probably has a .zip extension.

How does that happen? At first, you might think, “who cares how it happens?” The problem is when you write a shell script or a program that runs on Linux, the completion gets dumb. Someone has to make Bash smart about each command line program and if you are the author then that someone is you.

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